Combination of beetroot and barley grass as a supplementary diet to enhance color brightness in koi fish seed (Cyprinus carpio L.)

Color is a key quality trait in koi (Cyprinus carpio L.) that can be enhanced through dietary carotenoids. This study evaluated the effects of beetroot and barley grass supplementation on color brightness of koi seed. Fish (5–7 cm) were reared for 28 days in 25-L tanks, five fish per tank, under three dietary treatments and one control group, each with three replicates. Diets containing beetroot and barley grass powders were fed at 5% of body weight per day. Coloration was assessed weekly using a visual scoring method to obtain relative color brightness, and growth performance was recorded. Data were analyzed using one-way ANOVA (p < 0.05). The combination of beetroot and barley grass significantly increased relative yellow–orange–red hues brightness (p = 0.048). The 10% beetroot + 10% barley grass diet resulted the highest improvement (7.02 ± 3.38%), although not significantly different from the 5% beetroot + 15% barley grass diet (2.81 ± 3.22%). Both treatments outperformed the 15% beetroot + 5% barley grass diet (2.46 ± 0.61%) and the control (0.35 ± 0.61%). No significant effects were found on growth performance. These results indicate that balanced beetroot and barley grass supplementation can enhance koi color brightness.